Looking at the real-time satellite tracking
applet, I noticed that with a couple of exceptions it
appears that every satellite you list, including Chandra
appears in one of two basic orbital shells. One of these
being very close to the Earth, and the other being somewhat
farther away.

My questions are:
-Is it accurate that satellites fall into these two groups?
Or is it just the representation of the applet that is making
it look like this?
-What is the basic rationale for the two distances?
-Is there an international body that regulates where
somebody gets to put a satellite?

A:

Your impression that satellites fall into two basic orbital
shells is correct. The reason is the belts of high-energy
particles trapped in the Earth's magnetic fields (Van Allen
radiation belts). The radiation belts become important at
around 1000 km, so most spacecraft are in orbits below the
belts. The only ones higher than that and below geostationary
Earth orbit have to have a real good reason to be there. In
Chandra's case, the reason was improved observing efficiency,
with the trade-off that it is impossible to service it from
the Space Shuttle.
The International Telecommunication Union regulates locations
in the geostationary orbit for satellites which transmit in
the public bands (C, Ku, etc). There is no regulation of
orbit positioning, just of radio frequency emissions.